Regulation of free-piston motor compressors



Dec. 22, 1936. H, JNlCKE REGULATION 0F FREE-PISTON MOTOR COMPRESSORS Filed Feb. 23, 1935 /n vento/1 750m, a u u Patented Dec. 22, 1936 UNITI-:D ASTATI-:s

PATENT OFFICE REGULATION F FREE-PISTON MOTOR COMPRESSORS many Application February-Z3, 1935, Serial No. 7,786

In Germany March 9, 1934 11i-claims. (cl. 23o-5s) My invention relates to free piston motor compressors and has for one of itsl objects to provide means whereby the power absorption and delivery of the compressor chambers and/or additional chambers including pneumatic or other buffers can be controlled and regulated in 'a manner such that the output of the compressor can be adapted to the requirements of each individual case.

In my copendlng U. S. application Serial No.

710,483 I have disclosed a method of controlling a free piston motor compressor by varying the length of stroke and the pressures thereof, e. g.

the suction or discharge pressure, or both these pressures combined. My copenmng U. S. application Ser. No. 7,787 discloses the regulation of a free piston motor compressor by means of a variation of the pressures, i. e. the suction or delivery pressure or both these pressures combined,

0 and of the fuel supply to the motor cylinder of themotor compressor in a. manner such that the piston stroke remains always approximately constant; While my copending U. S. application Ser. No. '1,788 discloses the regulation of a free 25 piston motor compressor by the simultaneous variation of at least two of the variables, which at a predetermined constant stroke of the piston determine the output of the compressor as well as the return energy in such a manner' that 30 the portion of the total return energy which is available for the compression of the motor charge must always remain approximately constant.

In free-piston motor compressors comprising, 35` besides the combustion chamber of the motor one or more compressor chambers, and one or more freely reciprocating pistons, it has already been suggested to vary the length of stroke of the p pistons in order to vary the performance of the 40 compressor.- However such variation of stroke involves certain drawbacks as thereby the control of the motor part which is derived from the movement of the pistons, is subjected to undesirable variations. 45 It is an object of the present invention to render possible a variation of the compressorl performance within wide limits while keepingstroke of the pistons nevertheless remains substantially constant.

In some cases the amount of energy taken up or delivered by additional (subsidiary) chambers such as for instance pneumatic buffers, 5 which store compression energy during one stroke and deliver it during the subsequent stroke may be varied in a similar manner and for the same purpose, the energy thus delivered together with the energy which is released 10 during the return stroke in the compressor proper serving to compress the charge in the motor cylinder.

' The regulations to be effected according to this invention, i. e., the variation of the clearance l5 and of the quantity of fuel supplied to the motor cylinder per power stroke, may be effected either manually or automatically, or one of them may be effected manually, the other automatically.

Manual regulation is adopted, for instance, if there arise comparatively few or slow variations of the demand fo'r compressed gas, or if the requirements as tothe exactitude of regulation are not high. In such regulation the variation of the clearance volume as well as the `variation of the fuel supply may be eected by one and the same regulating member (a hand wheel, a lever, or the like) so that each regulating operation requires only the actuation of this member.

If both regulations are carried out automatically, they may be inuenced by variations of a single source of power, for instance by the pressure existing in a storage tank arranged in series with the compressor. It is however also possible to render the two regulations dependent from two separate sources of power, for instance to vary the clearance volume in dependency from the pressure in the storage tank, while regulating the fuelsupply to the motor cylinder in dependency from the stroke in such manner that 40 the stroke remains substantially constant.

I will now describe my invention more fully with reference to the drawing affixed to this specification and forming part thereof, which illustrates diagrammatically by way of example several embodiments of this invention.

In the drawing,

Figs. 1 and 3 are longitudinal sections of one half of a free-piston compressor with pistons reciprocating in opposite directions.

While Fig. 2 is a partial longitudinal section of another form of the compressor proper.

Fig. 4 is a diagram showing pressures plotted against stroke, for a compressor as shown in Figs. 1 or 2, 55

Fig. 5 is another diagram showing pressures plotted against stroke` for the pneumatic buffer illustrated in Fig. 3.

Referring to the drawing and first to Figs. 1 A

'a pinion I6 which is mounted to rotate in a nxed position at the casing I. The left hand motor piston 4 (Fig. 3) controls the scavenging ports 6, and the right hand motor piston 4 (Fig. 1) controls the exhaust ports 1 formed in the wall of the motor cylinder. The residual compressed gas which remains over in the clearance spaces of the compressor chamber at the end of each power stroke, expands and forces the masses (pistons) 4, 5 towards each other. When the pressure in the compressor cylinders has dropped to equal the suction pressure, fresh gas is drawn in through the suction valves 8 and, at the same time, the charge in the combustion chamber 2 of the motor cylinder is compressed. Toward the end of the return stroke liquid fuel is injected into the combustion chamber through pipe 22 and injection nozzle 23 by means of a fuel pump having a piston 2l) and a cylinder 2|, and the mixture is Iignited. The fuel pump which is more fully described in my copending application Ser. No. 710,483, is operated by a cam 24 formed on the rack I5 which, when the piston is near the end. of its inward stroke, turns a rocker 25 which displaces the pump piston 20 against a spring 26. The products of combustion in the motor cylinder now force the pistons apart, the gas which has been drawn into the compressor cylinders, is compressed and conducted to a storage tank I3 through delivery valves 9, delivery pipes I0 and delivery main I I. A pipe I4 distributes the compressed gas to the individual stations where it is required. A spring-loaded check valve I2 is provided in thel main II for maintaining the compression pressure in the compressor cylinders 3 at a denite minimum even if the pressure in the tank |3'should be lower than this minimum, for instance in consequence of heavy tappings of compressed gas, or when the compressor is started.v The check valve I2 may simply consist of a valve body which a spring tends to close, while the gas pressure prevailing in the main II tends to open the same. Since the force of the spring acting upon the valve body always can be maintained constant, the gas pressure prevailing in the main II also must have a predetermined minimum value in order to lift the valve body from its seat so as to open the valve.

The amount of fuel supplied to the motor cylinder per power stroke is here controlled automatically in a known manner in dependency from the pressure in the storage tank I3 by turning the pump piston. To this end a spur gear 30 is rigidly connected to the pump piston 20. A rack 3i meshing with this spur gear supports a piston 32 mounted to slide in cylinder 33. A compression spring 34 acts on one face of the piston while the pressure in the tank I3 through pipe 35 acts on its other face. In this manner the position of the piston' 32 is determiner: by the pressure m the tank la and y consequently the amount of fuel delivered at each stroke of the pump is a function of this pressure.

Figs. 1 and 2 also illustrate examples for the regulation of the compressor performance by -a y 41 engages in the spur gear. The piston 41 is acted upon by the pressure in tank I3, against the action of a spring 48. If the pressure in the tank i3 rises beyond the normal, i. e., if the output of the compressor exceeds the demand for compressed gas, the piston 41 is moved downwardly against the pressure of spring 48 and turns the spur gear 45, whereby the piston 42 ismoved to the right, the clearance of the cylinder is increased and the output of the compressor is reduced in proportion.

In the modification illustrated in Fig. 2 a casing 50 mounted on the cover 40 of the compressor cylinder forms three compartments 5I, 52, 53. Each compartment communicates 4with the compressor chamber 3 through a port 54, 55, 56, respectively.` These ports are controlled by a slide valve 51 which is formed with slots 58,59. 60 diering in length. When'the slide valve descends in the direction of arrow a, the compartments 5I, 52, 53 are successively connected to the compressor chamber, while, when the slide valve rises in the direction of arrow b, they are cut off in the opposite sequence. By the connection and disconnection of these compartments the clearance of the compressor is varied.

The slide valve 51 may be actuatedI by hand or it may, for instance like the rack 46 in Fig. 1, be controlled automatically in dependency from the pressure in the tank I3.

In Fig. 4 the variation of the diagram showing pressures plotted against strokes is illustrated for the Aregulation of the performance by variation of the clearance. The lines A B C D A show the compressor diagram for normal performance. 'I'he gas is compressed from the suction pressure p1 to the delivery pressure p2. 'I'he volume of the clearance corresponds to line VT. On increasing the clearance VT for normal operation by the amount v'r, the new diagram A L C M A is obtained. 'I'he performance represented by line L C is less than the normal performance corresponding to line B C.

Fig. 3 shows a free-piston compressor in which, in addition to the compressor-space 3, a pneumatic buffer is provided comprising a'cylinder 6I and piston 62. The amount of energy absorbed by the buffer during the outward stroke of the piston and delivered to it during the return stroke is regulated by varying the buffer clearance at substantially constant stroke of the flying mass. To this end the cover of the buifer cylinder is formed as a piston 63, which may be adjusted by hand or automatically, like the piston 42 in Fig. 1 for instance in dependency upon the pressure in storage tank i3. I

Instead of the slidable cylinder cover separate compartments might be provided for connection and disconnection, as described above.

Fig. 5 shows the diagram of such a buifer with pressures plotted against stroke. Assuming the initial pressure pn to be constant, if the clearance has the small volume VT, compression occurs along line N and the energy absorbed and delivered by the buffer then corresponds to the area N O P Q N. If the clearance volume is increased by vT, compression occurs along the line N R which extends below line N O, and the lower energy of the buffer is now represented by the area N R P Q N.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

I claim:-

1. A free piston motor compressor comprising in combination a motor` cylinder and at least one compressor cylinder arranged on either sideA thereof, and at least one buffer cylinder and a member adapted to regulate both the variation of volume 'of the clearance in said compressor cylinders and said buffer cylinder and the fuel supply to said motor cylinder.

2. A free piston motor compressor comprising in combination a motor cylinder, and at least one compressor cylinder arranged on either side thereof, members for varying the clearance volume in said compressor cylinders and for regulating the fuel supply to said motor cylinder, means for storing gas compressed in said compressor cylinders and a common means arranged to be influenced by the pressure in said gas storingmeans for moving both said members.

3. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, the pistons arranged on the same side of the motor cylinder being operatively connected with each other, means for varying the volume of the clearance of the said compressor cylinders and means for at the same time varying the supply of fuel to said motor cylinder in such manner as to keep the lfree piston stroke substantially constant.

4. A free piston motor compressor comprising in combination, a motor cylinder, at least one compressor cylinder arranged on either side thereof and at least one buffer cylinder, a free piston in each cylinder, the pistons arranged on the same side of the motor cylinder being operatively connected with each other, means for varying the volume of the clearance of the said compressor cylinders and the said buffer cylinder and means for at the same time varying the supply of fuel to said motor cylinder in such manner as to keep the free 'piston stroke substantially constant.

5. A free piston motor compressor comprising in combination. a motor cylinder and at least one compressor cylinder arranged Aat either side thereof, a free piston in each cylinder, the pislons arranged on the same side of the motor cylinder being operatively connected with each other, means for varying the volume of the clearance of the said compressor cylinders, means for at the same time varying the supply of fuel -to said motor cylinder in such manner as to keep the free piston stroke substantially constant, and a single lmember adapted to regulate the variation of the clearance volume of said compressor cylinders as well as of the supply of fuel to said motor cylinder.

6. A free piston motor compressor comprising in combination, a motor cylinder, at least one compressor cylinder arranged on either side thereof and at least one buffer cylinder, a free piston in each cylinder, the pistons arranged on the same side of the motor cylinder being operatively connected with each other, means for varying the volume of the clearance of the said compressor cylinders and the said buffer cylinder, means for at the same time varying the supply of fuel to said motor cylinder in such manner as to keep the free piston stroke substantially constant, and a single member adapted to regulate the variation of the clearance volumes of said compressor and buffer cylinders as well as of the supply of fuel to said motor cylinder.

7. A free piston motor compressor comprising in combination, a motor cylinder and at least v one compressor cylinder arranged on either side motor cylinder in such manner as to keep theA free piston stroke substantially constant, and a single source of power for moving all said means.

8. A free piston motor compressor comprising in combination, a motor cylinder, at least one compressor cylinder arranged on either side thereof and at least onev buffer cylinder, a free piston in each cylinder, the pistons arranged on the same side of the motor cylinder being operatively connected with each other, means for varying the volume of the clearance of the said compressor cylinders and the said buffer cylinder, means for at the same time varying the supply of fuel to said motorv cylinder in such manner as to keep the free piston stroke substantially constant, and a single source of power for moving all said means.

9. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, the pistons arranged on the same side of the motor cylinder being operatively connected with each other, means for varying the volume of the clearance of the said compressor cylinders, means for at the same time varying the supply of fuel to said motor cylinder in such manner as to keep the free piston stroke substantially constant, and means for accumulating the gas compressed in said compressor cylinders, the pres sure in said gas accumulating means constituting the only source of power for moving 'both the clearance volume and the fuel supply varying means.

- 10. A free piston motor compressor comprising in combination, a motor cylinder, at least one compressor cylinder arranged on either side thereof and at least one buffer cylinder, a free piston in each cylinder, the pistons arranged on the same side of the motor cylinder being operatively connected with each other, means for varying the volume of the clearance of the said compressor cylinders and the said buffer cylinder, means for at the same time varying the supply of fuel to said motor cylinder in such manner as to HERMANN JNICKE. 

